Summary of work: The pattern of regional cerebral blood flow assessed during PET activation with a face matching task was correlated with performance accuracy in both healthy young and elderly subjects. The pattern showed higher activity in the left fusiform and lingual gyri and right frontal association regions with relatively lower activity in lateral occipitotemporal regions, bilaterally. Two cerebral metabolic patterns characteristic of Alzheimer's disease (AD) were identified using regional covariance analysis of resting state brain glucose metabolism (rCMRglc). Expression of these patterns distinguished AD patients from patients with frontotemporal dementia and were correlated with specific cognitive deficits in the AD group. Premorbid intellectual ability was inversely correlated with rCMRglc in several regions of association cortex in AD patients. Among AD patients, early age at onset of dementia was related to greater impairment on measures of visuospatial function. AD patients with a family history of dementia showed greater rCMRglc deficits in the frontal association regions. Further, a unique neuropsychological profile was observed for a subgroup of dementia of the Alzheimer type (DAT) patients with early prominent visual disturbances characterized by severe visuospatial difficulties but better memory performance than typical AD patients. These visual variant AD patients also showed greater hypometabolism in parieto-occipital and calcarine cortices with relative sparing of paralimbic regions compared to typical AD patients. Postmortem pathology of one AD visual variant patient showed a distribution of senile plaques and neurofibrillary tangles consistent with the pattern of metabolic deficit in the visual variant AD group. Studies of visuospatial attention during visual search showed incremental slowing of reaction time with parametric increases in attentional distracters. This attentional slowing was greater in healthy elderly than young controls. AD patients showed less benefit than controls with decreasing cue size in a visual attention task. Long-term memory and orientation decline with age among non-demented Down's syndrome adults, whereas language and other functions remain preserved. Further, basic language skills were inversely correlated with apolipoprotein E4 genotype in non-demented DS adults. Despite poor figural reproduction across multiple learning trials, AD patients with both mild and moderate to severe dementia showed some acquisition of visual material during figural reproduction that predicted recognition performance and was unrelated to degree of visuospatial impairment.